The present invention relates to a method and apparatus for transferring magnetic signals from a master sheet to copy sheets which constitutes a novel improvement over the system disclosed in U.S. Pat. No. 3,721,775 which is assigned to the same assignee as the present application.
Magnetic sheets on which information is magnetically recorded in the form of, for example, a spiral recording track, in conjunction with a magnetic reader for the sheets, constitute a system which is especially suitable for use as a teaching aid. Both video and audio signals may be recorded on the sheets, to provide, for example, a visual reproduction of a picture and an audio narrative description of the picture. Of course, the sheets may be utilized to record only video or only audio information. An advantage of the system is that the copy sheets may be produced at very low cost.
To produce the copy sheets, the video and/or audio information is magnetically recorded on a master sheet which is typically formed of a polyester substrate coated with a magnetic material such as a ferric oxide. The copy sheets are formed of a paper substrate which is also coated with a magnetic material. To transfer the magnetic signals from the master sheet to a copy sheet, the master and copy sheets are pressed together with the magnetic coating in close contact and a rotating magnetic field is applied through the plastic substrate of the master sheet. Thereafter, the copy sheet is removed from the master sheet. The copy sheet is preferably perforated to provide indexing holes simultaneously with performing the magnetic transfer.
In the apparatus heretofore employed to perform the magnetic transfer operation, the master sheet is placed on a table with the magnetic coating thereof facing upwardly. The copy sheet is then slid along the table with the magnetic coating thereof facing downwardly onto the master sheet. After the transfer operation, the copy sheet is slid over and off of the master sheet into a receiving tray and another copy sheet is slid onto the master sheet for transfer.
The problem in this system is that when the copy sheet is slid off the master sheet in contact therewith magnetic transfer continues from the master sheet to the copy sheet in such a manner as to induce magnetic signals in the coating of the copy sheet which do not constitute usable information and which appear as noise when the copy sheet is inserted in reader for reproduction of the visual and/or audio signals.